1. Field of Invention
The present invention relates to a screwdriver and, more particularly, to a screwdriver for exerting an adjustable maximum value of torque.
2. Related Prior Art
As disclosed in Taiwanese Patent Publication No. 335757, a conventional screwdriver for exerting an adjustable maximum value of torque includes a handle 10, a driver 20, a follower 30, a shaft 40, a spring 50, a restraining ring 60, an adjusting element 70 and a sleeve 80. The driver 20 is non-rotationally located in the handle 10 while the follower 30 is rotationally located in the handle 10. The follower 30 includes teeth 31 for engagement with teeth 21 of the driver 20. The shaft 40 is inserted through the handle 10, the driver 20, the follower 30, the shaft 40, the spring 50, the restraining ring 60 and the adjusting element 70. The shaft 40 can be rotated relative to the driver 20 but cannot be rotated relative to the follower 30. A bit can be connected to a free end of the shaft 40 which extends from the handle 10. The spring 50 is compressed between the follower 30 and the ring 60. The ring 60 is located against the adjusting element 70 which includes a thread engaged with a thread of the handle 10. By spinning the adjusting element 70 relative to the handle 10, the stress loaded in the spring 50 is adjusted, and so is the extent to which the follower 30 is engaged with the driver 20, and so is the maximum value of torque that can be transferred to the follower 30 from the driver 20. The sleeve 80 is located around the handle 10 and the adjusting element 70.
There are problems encountered during the use of the conventional screwdriver. At first, the cost is high because of the use of the sleeve 80 around the handle 10 and the adjusting element 70 to avoid unintentional spinning of the handle 10 relative to the adjusting element 70.
Secondly, the adjustment of the maximum value of torque is inconvenient because the sleeve 80 must be detached from the handle 10 to allow the spinning of the handle 10 relative to the adjusting element 70 and then connected to the handle 10 to avoid unintentional spinning of the handle 10 relative to the adjusting element 70.
Thirdly, there is no means for compensating decrease of the elasticity of the spring 50 that would otherwise affect the precision of the indication of the maximum value of torque.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.